From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Subject: Re: [PATCH v6 2/2] arm64/crash_core: Export TCR_EL1.T1SZ in vmcoreinfo References: <1589395957-24628-1-git-send-email-bhsharma@redhat.com> <1589395957-24628-3-git-send-email-bhsharma@redhat.com> From: James Morse Message-ID: <7abd195f-2091-0ef9-2e0b-4a8bf2cf820e@arm.com> Date: Wed, 1 Jul 2020 12:59:39 +0100 MIME-Version: 1.0 In-Reply-To: <1589395957-24628-3-git-send-email-bhsharma@redhat.com> Content-Language: en-GB List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Bhupesh Sharma , linux-arm-kernel@lists.infradead.org, x86@kernel.org Cc: Mark Rutland , Kazuhito Hagio , Ard Biesheuvel , Catalin Marinas , Steve Capper , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Dave Anderson , bhupesh.linux@gmail.com, Will Deacon Hi Bhupesh, On 13/05/2020 19:52, Bhupesh Sharma wrote: > vabits_actual variable on arm64 indicates the actual VA space size, > and allows a single binary to support both 48-bit and 52-bit VA > spaces. I'd prefer the commit message not to refer to this 'vabits_actual' thing at all. By the time a git-archaeologist comes to read this, it may be long gone. Ideally this would refer to: TCR_EL1.TxSZ, which controls the VA space size, and can be configured by a single kernel image to support either 48-bit or 52-bit VA space. > If the ARMv8.2-LVA optional feature is present, and we are running > with a 64KB page size; then it is possible to use 52-bits of address > space for both userspace and kernel addresses. However, any kernel > binary that supports 52-bit must also be able to fall back to 48-bit > at early boot time if the hardware feature is not present. > > Since TCR_EL1.T1SZ indicates the size offset of the memory region > addressed by TTBR1_EL1 (and hence can be used for determining the > vabits_actual value) it makes more sense to export the same in > vmcoreinfo rather than vabits_actual variable, as the name of the > variable can change in future kernel versions, but the architectural > constructs like TCR_EL1.T1SZ can be used better to indicate intended > specific fields to user-space. > > User-space utilities like makedumpfile and crash-utility, need to > read this value from vmcoreinfo for determining if a virtual > address lies in the linear map range. > > While at it also add documentation for TCR_EL1.T1SZ variable being > added to vmcoreinfo. > > It indicates the size offset of the memory region addressed by TTBR1_EL1 > diff --git a/arch/arm64/kernel/crash_core.c b/arch/arm64/kernel/crash_core.c > index 1f646b07e3e9..314391a156ee 100644 > --- a/arch/arm64/kernel/crash_core.c > +++ b/arch/arm64/kernel/crash_core.c > @@ -7,6 +7,14 @@ > #include > #include > #include > +#include > + > +static inline u64 get_tcr_el1_t1sz(void); > + > +static inline u64 get_tcr_el1_t1sz(void) > +{ > + return (read_sysreg(tcr_el1) & TCR_T1SZ_MASK) >> TCR_T1SZ_OFFSET; > +} > > void arch_crash_save_vmcoreinfo(void) > { > @@ -16,6 +24,8 @@ void arch_crash_save_vmcoreinfo(void) > kimage_voffset); > vmcoreinfo_append_str("NUMBER(PHYS_OFFSET)=0x%llx\n", > PHYS_OFFSET); > + vmcoreinfo_append_str("NUMBER(TCR_EL1_T1SZ)=0x%llx\n", > + get_tcr_el1_t1sz()); > vmcoreinfo_append_str("KERNELOFFSET=%lx\n", kaslr_offset()); > vmcoreinfo_append_str("NUMBER(KERNELPACMASK)=0x%llx\n", > system_supports_address_auth() ? (I think second guessing the kernel memory map is a sisyphean effort), but this register isn't going to disappear, or change its meaning!: Reviewed-by: James Morse You may need to re-post this to get the maintainer's attention as its normally safe to assume patches posted before rc1 no longer apply. (in this case, this one does) Thanks, James _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec